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Full text of "Linear Technologies-DN9612 Bit Rail-to Rail Micropower DA Csinan SO-8OCR"

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DESIGN 
NOTES 



LTC1 451/52/53: 12-Bit Rail-to-Rail Micropower DACs in an SO-8 

Design Note 96 

Hassan Malik and Jim Brubaker 



The UC®1451, LTC1452 and LTC1453 are complete, 
single supply, rail-to-rail voltage output 12-bit digital-to- 
analog (DAC) converters. They include an output buffer 
amplifier and a space saving SPI compatible three-wire 
serial interface. There is also a data output pin that allows 
daisy-chaining multiple DACs. These DACs use a propri- 
etary architecture which guarantees a DNL (Differential 
Nonlinearity) error of less than 0.5LSB. The typical DNL 
error is about 0.2LSB as shown in Figure 1. There is a 
built-in power-on reset that resets the output to zero 
scale. The output amplifier can swing to within 5mV of 
Vcc when unloaded and can source or sink 5mA even at 
a 4.5V supply. These DACs come in an 8-pin PDIP and 
SO-8 package. 

5V and 3V Operation 

The LTC1 451 has an on-board reference of 2.048V and a 
nominal output swing of 4.095V. It operates from a single 
4.5V to 5.5V supply dissipating 2mW (lcc(TYP) = 400|aA). 

The LTC1452 is a multiplying DAC with no on-board 
reference and a full-scale output of twice the reference 
input. It operates from a single supply that can range from 
2.7V to 5.5V. It dissipates 1 .1 25mW (Icc(typ) = 225liA) at 
a 5V supply and a mere 0.5mW (IccrjYP) = 1 60liA) at a 3V 
supply. 



clk|T} 



The LTC1453 has a 1.22V on-board reference and a 
convenient full scale of 2.5V. It can operate on a single 
supply with a wide range of 2.7V to 5.5V as shown in 
Figure 2. It dissipates 0.75mW (IqcfTYP) = 220pA) at a 3V 
supply. The digital inputs can swing above Vcc for easy 
interfacing with 5V logic. 

True Rail-to-Rail Output 

The output rail-to-rail amplifier can source or sink 5mA 
over the entire operating temperature range while pulling 
to within 300mV of the positive supply voltage or ground. 
The output swings to within a few millivolts of either 

£T, LTC and LT are registered trademarks ot Linear Technology Corporation. 



MICRO- 
PROCESSOR 











TO NEXT DAC 
FOR DAISY-CHAINING 





Figure 2. The 3V LTC1453 is SPI Compatible 
and Talks to Both 5V and 3V Processors , 



— HI Vcc 



es/LDQ] 1 | — 



Dour [7} 



0.5 



g o.o 



-0.5 



512 1024 1536 2048 2560 3072 3584 4095 
CDDE 



Figure 1 . Proprietary Architecture Guarantees Excellent DNL 



02/95/96 



Circle No. 53 



supply rail when unloaded and has an equivalent output 
resistance of 50Q when driving to either rail. The output 
can drive a capacitive load of up to 1 0OOpF without 
oscillating. 

Wide Range of Applications 

Some of the applications for this family include digital 
calibration, industrial process control, automatic test 
equipment, cellulartelephones and portable battery-pow- 
ered applications where low supply current is essential. 
Figure 3 shows how to use an LTC1453 to make an opto- 
isolated digitally controlled 4mA to 20mA process con- 
troller. The controller circuitry, including the opto-isola- 
tor, is powered by the loop voltage that can have a wide 



Flexibility, True Rail-to-Rail Performance and 
Micropower; All In a Tiny SO-8 

The LTC1451, LTC1452 and LTC1453 are the most flex- 
ible micropower, stand alone DACs that offer true rail-to- 
rail performance. This flexibility along with the tiny SO-8 
package allows these parts to be used in a wide range of 
applications where size, power, DNL and single supply 
operation are important. 

Table 1. LTC Serial Voltage Output DACs 



- x n r\\ i i - 



used forthe digitally controlled OmA to 1 6mA current. Rs 
is a sense resistor and the LT®1077 op amp modulates 
the transistor Q1 to provide the 4mA to 20mA current 
through this resistor. The potentiometers allow for offset 
and full-scale adjustment. The control circuitry con- 
sumes well under the 4mA budget at zero scale. 



Part 


V C c Range 


Reference 


Full Scale 


Ice 


LTC1451 


4.5V to 5.5V 


2.048V-lnternal 


4.095V 


400nAat5V 


LTC1452 


2.7V to 5.5V 


External 


2xREF 


225^A at 5V 




4./0V 10 

15.75V 


z.u4Bv-internai 
(2.5V to 12V- 
External) 


ZU48V 
(2.5V to 
12V) 


abupAatbv 



VlOOP 
3.3V TO 30V 




CLK 
CS/LD 



K. 50011 I 

— J^O— VW 4N28 



Figure 3. 4mA to 20mA Process Controller Has 3.3V Minimum Loop Voltage 



For literature on our Digital-to-Analog Converters, 
call 1-800-4-LINEAR. For applications help, 
call (408) 432-1900, Ext. 525 



Linear Technology Corporation 

1630 McCarthy Blvd., Milpitas, CA 95035-7487 

(408) 432-1900 • FAX: (408) 434-0507 • TELEX: 499-3977 



LT/GP 0285 1 90K • PRINTED IN THE USA 
© LINEAR TECHNOUOGY CORPORATION 1995